1. Field of the Invention
This invention relates to an ink jet printer and an image printing system as well as printing method therefor, and more particularly to an ink jet printer for printing a print image on a print medium by scanning a print head (ink jet head) having a plurality of nozzles arranged in a Y-axis direction, assuming that two axes orthogonal to each other on a two-dimensional rectangular coordinate system are an X axis and the Y axis, in directions along the X axis and the Y axis, relative to the print medium, and an image printing system incorporating the ink jet printer, as well as printing methods therefor.
2. Prior Art
Conventionally, in the ink jet printer of the above-mentioned kind employs a printing method (first printing method) described below, due to the merit of capable of making constant the amount of feed (head moving pitch) in the direction along the Y axis. For example, the present assignee has also proposed an ink jet printer of this kind (Japanese Laid-Open Patent Publication (Kokai) No. 10-250120). In the case of the first printing method, assuming that the head moving pitch and a nozzle pitch are represented by P and D, respectively, a printable dot (position thereof) R can be expressed by R=P×j+D×i. For example, as shown in FIG. 10A, assuming that the head moving pitch P is 4, and the nozzle pitch D is 3 (and hence the printable dot R=4j+3i), and four nozzles designated by circled numbers 1 to 4 in the figure (represented by i=0, 1, 2, 3 in the figure) are used, it is possible to print dots from a sixth dot from a reference position (position to be assumed by a nozzle of encircled number 1 during a first printing pass (Pass=1 in the figure)) in a continuous manner, i.e. without forming a break or unprinted dot between printed dots (see FIG. 10B). This fact is shown in FIG. 10B as OK from Step=6 (which is the number of dots representative of the distance “t” of each nozzle from the reference position).
However, according to this printing method, it is necessary to start printing operation from outside the actual printing area. For example, in the case of the illustrated example shown in FIGS. 10A and 10B, as indicated by “OK from Step=6”, the actual printing area is below the line indicated by OK (Step=6) in FIG. 10B. However, the printing operation has to be started after moving the print head to a position which is above, in the figure, than the line of OK, and in which the position assumed by the nozzle designated by encircled number 1 is the reference position t=0. In other words, this printing operation includes a portion which does not contribute to actual printing and hence is useless. Particularly, when the width of a print image in the direction along the Y axis (hereinafter referred to as “the Y-axis direction”), i.e. the width of lower part than the above-mentioned OK in the figure is small, the ratio of a useless portion of the printing operation becomes large relative to an effective portion of the same, so that the overall printing efficiency is degraded, which lowers the printing speed.
On the other hand, an ink jet printer has not been conventionally known which prints a print image on a print medium by scanning a print head (ink jet head) in X-axis and Y-axis directions relative to the print medium, while feeding the print medium in the X-axis direction. For example, an ink jet printer has not been known in which a continuous (tape-shaped) print medium is mounted such that the longitudinal direction thereof coincides with the X axis, and which performs printing by a plurality of nozzles (of the ink jet head) juxtaposed in the Y-axis direction while feeding the print medium in the X-axis direction.
If an attempt is made to print on the print medium, e.g. the tape-shaped one, by feeding the same in the X-axis direction, there arises a problem which cannot occur when the print medium is fed in the Y-axis direction. For example, as shown in FIGS. 16A, 16B, when a print head PH prints a unitary print image D1 by feeding the print medium in the X-axis direction designated by a thick arrow in the figure, the amount of movement (indicated by one dot chain line) for returning the print head to its origin or the home position (starting point) SP is large and it takes time before the print head is brought to this position, necessarily causing the lowered printing speed. Particularly, when the width of the print image in the Y-axis direction is large, the time for returning the print head to the home position tends to become large relative to the time required in feeding the print medium, so that the overall printing efficiency is degraded, which lowers the printing speed.